The invention relates to a method of radiotransmission in a danger alarm system.
Radio is an ideal transmission medium for use in buildings. Equipment using radiotechnology can be quickly installed and easily adapted to necessary requirements. One disadvantage, however, is the relatively short range of radio at carrier frequencies in the gigahertz band. When so-called “repeaters” are employed to enhance the range, the high energy consumption requires network-supplied equipment. This applies especially to radio equipment in the new “SRD” band between 868 and 870 Mhz. In equipment using repeaters for range enhancement, information must reach its destination in a short time by way of a number of stations. For purposes of building safety (fire alarm, intrusion protection) this time amounts to several seconds, and in building automation (lighting equipment) the time is less than one second. To ensure this, powerful computers are required to find the correct route through a widely ramified network in which probabilities are examined, paths are pre-selected, statistics are set up, etc. This requires storage space, computer performance, and last but not least, an amount of electrical energy for which not even a year's supply by batteries is suitable at the present time.
EP 0,911,775 discloses a method of radiotransmission in a danger alarm system, suitable for battery operation. Here, in response to routine signals from peripheral elements, the center issues a receipt signal, which is used by transmission-ready peripheral elements as starting signal for transmission of alarm data to the center. In the case of several available radio channels, routine signals are issued and receipt signals awaited in successive channel time slots until a receipt signal is received in a time slot of the connection. This receipt signal is received by a transmission-ready peripheral element which, on the same radio channel identified as free, then sends its alarm data to the center in the next time slot for alarm data transmission. This method is distinguished by minimal energy consumption in combination with short monitoring and reaction times in the range of seconds. One disadvantage is the comparatively costly procedure and the long reaction times in repeater operation. Since the participants of the system must keep themselves synchronous, they must synchronize their internal clocks. This results in relatively heavy radio traffic and consequently the need for several radio channels.
DE 19905 316 discloses a data transmission system, in particular for consumption data detection, comprising at least one transmitter and one receiver for receiving data packages transmitted at time intervals from a respective transmitter. Here, the receiver includes a time control means for temporal control of its reception operation, estimating the point in time of the next data transmission currently awaited on the basis of target values for the time intervals of successive data packages, and in each instance switching the receiver reception-ready temporarily during a tolerance interval containing the estimated point in time. The length of the data package is here limited to the tolerance interval.